JP3349141B2 - Liquid crystal display device and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device which requires a transition of liquid crystal molecules from an initial orientation to a predetermined displayable orientation prior to display. The present invention relates to an improvement in a driving method of a liquid crystal display device for performing transition.

[0002]

2. Description of the Related Art Conventionally, various liquid crystal display devices have been proposed and put into practical use. In recent years, the spread of liquid crystal televisions is expected. A liquid crystal display device of a twisted nematic mode using a nematic liquid crystal, which is widely used, has disadvantages such as a slow response and a narrow field of view. The liquid crystal display device of the in-horizontal plane driving mode having a wide field of view has a difficulty in response speed and aperture ratio. A liquid crystal display device of a ferroelectric liquid crystal mode (hereinafter, referred to as FL) having a quick response and a wide viewing angle.
C-type liquid crystal display devices) have major drawbacks in shock resistance, temperature characteristics, and the like.

[0003] For example, Japanese Patent Application Laid-Open No.
No. 54 and IEICE Technical Report EDI98
The liquid crystal display device of the optical compensation bend mode (or the optical compensation birefringence mode) (hereinafter referred to as OCB type liquid crystal display device) proposed on p. For example, application to a liquid crystal television as a transmission type or reflection type liquid crystal display device is expected.

FIG. 7 shows an example of an OCB type liquid crystal display device. The liquid crystal panel 2 includes an array substrate 3 a having a transparent pixel electrode 4 a formed on the surface thereof, and a transparent counter electrode 4
b, and a liquid crystal layer 7 sandwiched between the array substrate 3a and the counter substrate 3b. On the inner surfaces of the substrates 3a and 3b on which the pixel electrodes 4a and the counter electrodes 4b are respectively provided, a liquid crystal alignment film 6 made of polyimide is provided.
a and 6b are formed. Each of the liquid crystal alignment films 6a and 6b has been subjected to a rubbing treatment, and is arranged so that the rubbing directions are parallel to each other. The liquid crystal layer 7 is filled with a nematic liquid crystal material having a positive dielectric anisotropy. When no voltage is applied between the electrodes 4a and 4b, the pretilt angles of the liquid crystal molecules 7a on the surfaces of the substrates 3a and 3b are about several degrees to 10 degrees in opposite directions to each other, and the liquid crystal molecules 7a are shown in FIG. As shown in ()), an orientation (spray orientation) that is obliquely spread vertically and symmetrically on the same plane is shown.

In the OCB type liquid crystal display device, a relatively high voltage pulse (hereinafter referred to as a transition voltage pulse) is applied between the electrodes 4a and 4b in a short time when the main power supply of the device is turned on. The liquid crystal molecules 7a having a splay alignment as shown in FIG.
As shown in (b), a minute region showing bend orientation including bend orientation or twist orientation (hereinafter referred to as transition nucleus)
Occurs. By repeatedly applying the transition voltage pulse, the transition nucleus expands. The OCB type liquid crystal display device
The display can be performed by transferring all the liquid crystal materials in the liquid crystal layer 7 to the bend alignment. The OCB type liquid crystal display device performs display using a change in optical phase difference caused by a change in the degree of bend alignment of the liquid crystal molecules 7a caused by application of a display signal drive voltage. On the outer surface of the liquid crystal panel 2, a phase compensating plate 8 for enabling low voltage driving of the liquid crystal panel 2 and optically compensating for expanding the viewing angle is fixed with its optical axis in a predetermined direction. Be placed.

As described above, in the OCB type liquid crystal display device, the transition from the splay alignment to the bend alignment is initially promoted before entering the normal display driving mode, and the transition is performed in all the pixel regions of the liquid crystal panel. It must be completed in a short time. Further, the same processing is required before the display driving mode in the FLC type liquid crystal display device and the phase transition type liquid crystal display device. Therefore, these liquid crystal display devices have the following problems.

If the liquid crystal molecules are not sufficiently transferred to the orientation for display, good display cannot be obtained when the mode is shifted to the display driving mode. For example, in the OCB-type liquid crystal display device, the transition to the bend alignment is not reliably performed, and if a region of the splay alignment remains locally, the portion becomes a bright spot at the time of display driving and looks like a point defect. In addition, for a few seconds to several minutes after the start of the display driving, the display becomes entirely cloudy and the image is not stable. Therefore, it is necessary to surely complete the transition to the bend alignment before shifting to the display driving mode. However, even when a voltage pulse for transition is applied under the same conditions, transition nuclei do not occur at the same place and occur accidentally, so it has been difficult to surely terminate the transition in a short time.

When the main power of the apparatus is turned on, the backlight is turned on. In the case of a liquid crystal television, sound output from a speaker is also started at the same time. However, in a liquid crystal display device that needs to transfer the orientation of liquid crystal molecules in a liquid crystal layer to a predetermined orientation prior to display, it may take a long time to shift to display driving. During the transition period up to the display drive mode, that is, the transition processing period, turning on the backlight is a waste of energy.
In addition, displays with many point alignment defects and planar alignment defects due to untransferred or in the middle of transition, and blinking of the entire screen due to the application of pulse voltage for transition may cause discomfort and anxiety to the user. Also. In order to realize a liquid crystal display device having high image quality and being commercially excellent, it is necessary to make the above-mentioned defect state caused by the alignment transition invisible so as not to give a sense of incongruity.

In order to develop a liquid crystal display device for various uses, it is necessary to guarantee the operation of the device over a wide temperature range. In the OCB type liquid crystal display device, it is necessary to complete the above-described transition processing to the bend alignment in the operation guaranteed temperature range reliably and in a short time. For example, in a 10-type active matrix liquid crystal display device, the transition can be completed in a short time of 0.5 to 1 second at room temperature around 25 ° C., but in a low-temperature atmosphere of −10 ° C. to 0 ° C. , It takes a long time to process the entire liquid crystal layer to bend alignment,
It may take several minutes depending on the conditions. That is, for practical use, it is necessary to surely perform this transition processing within a short temperature, at most within a few seconds, in a wide temperature range similar to a general display device.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the initial alignment of liquid crystal molecules is different from the alignment for display as represented by an OCB type liquid crystal display device. It is an object of the present invention to provide a method for driving a liquid crystal display device, which is capable of terminating transition of liquid crystal alignment for display in a reliable and short time.

[0011]

A driving method of a liquid crystal display device according to the present invention comprises a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, and voltage applying means for applying a voltage to the liquid crystal layer. Comprising a liquid crystal panel, wherein the initial alignment of the liquid crystal layer is for a liquid crystal display device different from the alignment for display,
Prior to the display by the liquid crystal panel, a voltage is applied to the liquid crystal layer in the display area of the liquid crystal panel until the transition from the initial alignment to the alignment for display is completed. Preferably, it is determined that the transition has ended after the product of the growth rate of the minute region of the liquid crystal layer that has transitioned to the orientation for display and the voltage application time becomes larger than the area of the display region of the liquid crystal panel. For example, when the product of the growth rate and the voltage application time exceeds a predetermined value within a range of 1 to 2 times the area of the display area of the liquid crystal panel, it is determined that the transition has ended.

Since the speed of the transition depends on the temperature, the temperature of the panel is measured prior to the application of the voltage for causing the transition, and the voltage application time for the transition is set based on the obtained temperature. Then, excessive or insufficient voltage application can be prevented. In addition, when a voltage is applied to the liquid crystal layer during the time required for the liquid crystal layer in the display area to transition to the orientation for display at the lowest temperature within the preset operating temperature range, the transition is ensured in the entire operating temperature range. Can be completed.

To transfer the liquid crystal layer in the display area,
For example, a minute region occupied by the liquid crystal material that has been transferred to the orientation for display is generated for each pixel or each region including a predetermined number of pixels, and then the minute region is grown. For example, this minute region can be generated around a projection formed on the surface of the voltage applying means or a portion where the pretilt angle of the liquid crystal material provided on the liquid crystal alignment film is different from that of another portion. When this minute region is formed for each pixel, it can be determined that the transfer has ended after the product of the growth rate of the minute region and the voltage application time becomes larger than the area of the pixel. When one minute area is formed for a plurality of pixels, the product of the growth rate of the minute area and the voltage application time is
The end of the transition may be determined in the same manner by comparing the size of the number of pixels corresponding to one micro area.

The voltage for the transition is applied intermittently or continuously to the liquid crystal layer. In the case of a so-called transmission type liquid crystal display device having a backlight, it is preferable to turn on the backlight after the application of the voltage to the liquid crystal layer is completed. This method of driving a liquid crystal display device is useful for an optically compensated bend type liquid crystal panel in which the alignment for display is bend alignment and the alignment of the liquid crystal layer is changed from splay alignment to bend alignment prior to display.

A liquid crystal display device according to the present invention has a liquid crystal alignment film having a rubbed surface on its surface, and a pair of substrates arranged so that the liquid crystal alignment films face each other and the rubbing directions are the same. A liquid crystal panel including a liquid crystal layer sandwiched between a pair of substrates and voltage applying means for applying a voltage to the liquid crystal layer is provided, and a length of the substrate in a rubbing direction is longer than a length in a direction perpendicular to the rubbing direction. The growth speed of the minute region in the rubbing direction is higher than that in the direction perpendicular to the rubbing direction. Therefore, when the longitudinal direction of the substrate is parallel to the rubbing direction, the time required for the transfer can be greatly reduced. Also, if the length of the pixel in the rubbing direction is longer than the length in the direction perpendicular to it,
Similarly, the time required for transfer can be greatly reduced.

Another method of driving a liquid crystal display device according to the present invention is as follows.
A liquid crystal panel including a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, and a voltage applying unit for applying a voltage to the liquid crystal layer, and a backlight for irradiating the liquid crystal panel with light for display on the liquid crystal panel. Applying a voltage to the liquid crystal layer to transition the liquid crystal layer to an orientation for display, wherein the initial orientation of the liquid crystal layer is different from the orientation for display. Turning on the backlight after the application of the voltage for the transition is completed.

In a liquid crystal television, for example,
Output of broadcast audio is started when the main power is turned on. Thereby, the user is made aware that the device is being activated. Image display starts after the end of the transition. For example, the backlight is turned on only during a normal display driving mode, that is, when displaying an image. This driving method is particularly useful for an optically compensated bend-type liquid crystal display device in which the orientation of a liquid crystal layer is changed from a splay orientation, which is an initial orientation, to a bend orientation, which is an orientation for display, prior to display on a liquid crystal panel. . This driving method is used, for example, in a liquid crystal display device using an active matrix type liquid crystal panel having a switching element for each pixel. Preferably, when a predetermined time has elapsed from the start of the transition of the liquid crystal layer, it is determined that the transition has been completed, and the backlight is turned on.

In order to transfer the liquid crystal layer to a predetermined orientation in a short time, it is necessary to apply a voltage higher than that of the voltage signal for display of the liquid crystal panel, but it is equivalent to that of the display voltage signal. The transition can also be advanced by applying a voltage of. That is, it is not necessary to prepare a power supply device for each of the transition drive and the display drive, and an output voltage signal from the display drive power supply can be used as the transition voltage signal. In a liquid crystal display device having a cover for covering a liquid crystal panel, such as a notebook personal computer and a foldable mobile phone, it is preferable to detect the progress of the transition in synchronization with opening of the cover prior to turning on the backlight. . That is, it is determined whether or not the transfer is completed when the cover is opened, and if the transfer is completed, the backlight is turned on at that time. If the transfer is not completed, the backlight is turned on after the transfer is completed. The transition of the liquid crystal layer may be started when the cover is opened. The backlight is turned off in synchronization with the closing of the cover and a voltage is applied to the liquid crystal layer in order to maintain the alignment state of the liquid crystal layer. The backlight is turned on in synchronization with the opening of the cover and the application of the voltage is terminated. Is preferred.

When an input signal from the user is not recognized for a predetermined time, it is preferable to turn off the backlight and apply a voltage to the liquid crystal layer in order to maintain the alignment state of the liquid crystal layer. In this case, if an input signal from the user is recognized during application of a voltage for maintaining the alignment state of the liquid crystal layer, the application of the voltage is terminated and the backlight is turned on. Preferably, the user is notified of the progress or completion of the transition of the liquid crystal layer. For example, the user is notified by voice using a speaker, an optical signal or display using a lamp, a light emitting diode, an electroluminescence element, or the like. In the case of a liquid crystal television, when the main power supply is turned on, the application of a voltage to the liquid crystal layer and the output of broadcast audio by a speaker are started, and an audio signal indicating a transition state is superimposed on the broadcast audio signal. Is preferred.

Another liquid crystal display device of the present invention comprises a liquid crystal layer whose initial alignment is different from the alignment for display, a pair of substrates sandwiching the liquid crystal layer between them, and voltage applying means for applying a voltage to the liquid crystal layer. A liquid crystal panel including a liquid crystal panel, a backlight for irradiating the liquid crystal panel with light for display on the liquid crystal panel, and a voltage application unit for driving the voltage application unit to apply a voltage to the liquid crystal layer to transfer the liquid crystal layer to an orientation for display. The liquid crystal display further includes a transition control unit that determines the end of the transition of the liquid crystal layer, and a backlight control unit that turns on the backlight after the end of the transition.

This is useful for an optically-compensated bend-type liquid crystal display device in which the alignment for display is bend alignment and the alignment of the liquid crystal layer is changed from splay alignment to bend alignment prior to display. Further, it is useful for an active matrix type liquid crystal display device having a switching element for each pixel. Preferably, the display device further includes a switch for forcibly starting application of a voltage for transition of the liquid crystal layer by the voltage applying unit. When a display defect due to a transition defect is recognized in the liquid crystal panel, the liquid crystal layer is subjected to a transition process again by using this switch to eliminate the display defect.

Another driving method of the liquid crystal display device of the present invention is as follows.
An OCB type liquid crystal display device including a pair of substrates, a liquid crystal layer sandwiched between the substrates, and a liquid crystal panel including a voltage applying unit for applying a voltage to the liquid crystal layer, is provided prior to displaying an image. Measuring the temperature of the liquid crystal panel, determining the condition of the voltage pulse for changing the orientation of the liquid crystal layer to bend alignment based on the measured temperature, and applying the voltage pulse to the liquid crystal layer according to the determined condition. Applying.

In a preferred aspect of the present invention, in the step of determining the condition of the voltage pulse, the frequency of the voltage pulse is determined based on the measured temperature. At this time,
Preferably, the frequency of the voltage pulse is set higher on the high temperature side than on the low temperature side. For example, the frequency of the voltage pulse when the temperature is 20 ° C. or more is 2 to 5 Hz and 0 ° C.
The frequency of the voltage pulse in the following cases is 0.2 to 1 Hz. More preferably, the frequency of the voltage pulse at 20 ° C. or higher is 2.5 to 4 Hz, and the frequency of the voltage pulse at 0 ° C. or lower is 0.4 to 0.6 Hz.

In another preferred aspect of the present invention, in the step of determining the condition of the voltage pulse, the voltage value of the voltage pulse is determined based on the measured temperature. At this time, preferably, the voltage value of the voltage pulse is set higher on the low temperature side than on the high temperature side. In a further preferred aspect of the present invention, in the step of determining the condition of the voltage pulse, the frequency and the voltage value of the voltage pulse are determined based on the measured temperature.

In another preferred embodiment of the present invention, in the step of determining the condition of the voltage pulse, the pulse width of the voltage pulse is determined based on the measured temperature. The conditions of these pulses are continuously changed with respect to the temperature. Moreover, you may change it stepwise. For example, in the step of determining the condition of the voltage pulse, the condition of the voltage pulse determined for each of the divided predetermined temperature regions is set. For example, the operating temperature range for use is divided into two temperature ranges, a high temperature side and a low temperature side.

By providing an initial period in which the potential difference between the electrodes as the voltage applying means is set to approximately 0 V immediately before applying the voltage pulse to the liquid crystal layer, the transition can be completed in a short time. The initial period is preferably between 0.2 and 5 seconds. When voltage pulses are applied intermittently, it is effective to provide a period in which the potential difference between the electrodes is approximately 0 V between the pulses. The transition can be completed in a short time by applying the voltage pulse to all the pixels at once. In the case of a transmissive liquid crystal display device equipped with a backlight, it is preferable to turn on the backlight after the liquid crystal material in the liquid crystal layer transitions to bend alignment by applying a voltage pulse. This driving method is used, for example, in an active matrix type liquid crystal display device having a switching element for each pixel.

In another driving method of the OCB type liquid crystal display device of the present invention, prior to displaying an image, the liquid crystal layer is transferred to a bend alignment at a minimum temperature within a preset operating temperature range. The voltage pulse is applied to the liquid crystal layer in the entire operating temperature range according to the condition that the time for applying the voltage pulse is short. That is, the voltage pulse is applied to the liquid crystal layer over the entire operating temperature range using conditions suitable for a temperature at which a longer time application of the voltage pulse is required. This allows the transition to be completed in a relatively short time at any temperature used. For example, a voltage pulse with a fixed condition of one frequency selected from the range of 0.2 to 1 Hz, more preferably one selected from the range of 0.4 to 0.6 Hz is applied.

[0028] Still another liquid crystal display device of the present invention comprises an OC.
A liquid crystal panel comprising a pair of substrates, a liquid crystal layer sandwiched between the substrates, and a voltage application unit for applying a voltage to the liquid crystal layer; and a panel temperature detection unit for detecting a temperature of the liquid crystal panel. And pulse condition determining means for determining, based on the temperature of the liquid crystal panel detected by the panel temperature detecting means, the condition of the voltage applied by the voltage applying means to change the orientation of the liquid crystal layer to the bend orientation.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. In the following embodiments, an OCB type liquid crystal display device will be described as an example.

<< Embodiment 1 >> In this embodiment, an example of a method for reliably transferring the alignment state of a liquid crystal layer from an initial alignment to an alignment for display prior to display on a panel will be described with reference to the drawings. This will be described in detail.

In an OCB type liquid crystal panel as shown in FIG. 7, a pair of substrates 3a and 3b basically have liquid crystal alignment films 6a and 6b formed on the surface in contact with liquid crystal layer 7.
Are arranged so that the rubbing directions are parallel to each other. In an initial state in which no voltage is applied between the electrodes 4a and 4b, the liquid crystal molecules 7a in the liquid crystal layer 7 are in a splay state in which they are arranged substantially in parallel as shown in FIG. In order to display a panel, it is necessary to transfer the panel to a bend alignment state as shown in FIG. For this transition,
Conventionally, a voltage (for example, 25 V) relatively higher than the display drive signal is applied between both electrodes.

Since normal display cannot be performed during the application of the transition voltage pulse, it is desirable to shorten the period of the transition process in consideration of user convenience and the like.
When a voltage pulse for transition is applied, a fine region (transition nucleus) having a bend orientation is locally generated, and then gradually grows. When this transition nucleus is generated in the pixel, the transition to the bend orientation starts from this. For example, a transition nucleus forming part is provided on an auxiliary capacitance arranged near a gate line in a pixel. A transition nucleus can be generated at a desired location by providing a projection on the electrode or providing a region on the liquid crystal alignment film in which the pretilt angle of liquid crystal molecules located on the surface is different from that of the other location.

When the application of the transition voltage pulse is stopped and the drive signal for display is transmitted after the bend alignment region covers the entire pixel, a good display can be obtained. Since a transition nucleus is generated for each pixel for sufficient transition, it is necessary to apply a transition voltage pulse until the product of the growth rate of the bend-aligned region and the application time is equal to or larger than the pixel size. Here, the growth rate of the bend alignment region is shown in FIG.

[0034]

[Table 1]

As apparent from the figures and the table, the growth rate of the transferred bend alignment region depends on the temperature and the applied voltage, respectively. Further, the growth rate of the liquid crystal alignment film in the rubbing direction is faster than that in the direction perpendicular thereto. Therefore, the bend alignment region can be formed in a short time by making the longitudinal direction of the rectangular pixel coincide with the rubbing direction.

In a liquid crystal panel in which the longitudinal direction of the pixel is actually matched with the rubbing direction, the growth rate is 4000 μm.
At room temperature (25 ° C.) which is m / sec, the pixel size is 160
The voltage application time of the liquid crystal panel of μm × 50 μm is 0.0
Four seconds was sufficient. The pixel size is 450 μm ×
In the case of 150 μm, the voltage application time at room temperature of 0.12 seconds was sufficient. However, as described above, the growth rate differs depending on the temperature. If the application time of the voltage pulse for causing the transition to the bend orientation is excessive, normal display cannot be performed by an excessive amount. That is, it is a factor that wastes time for the user. In addition, if the transition to the bend orientation is insufficient, normal display may not be performed. Therefore, a temperature sensor is installed on the liquid crystal panel, and the time for applying the voltage is determined based on the measured panel temperature. According to this method, the transfer process can be performed in a proper time, and the excess or shortage of the process can be prevented.

The above-mentioned management of the transfer process by temperature requires additional cost for adding a temperature sensor and its control means. Therefore, from the viewpoint of preventing the shortage of the transition treatment, if the conditions required for transition to the bend orientation at the lowest temperature where the growth rate of the transition nucleus is the slowest in the operation guaranteed temperature range of the apparatus are set in advance, the temperature can be increased. Sufficient transfer processing is guaranteed without the need to mount a sensor. Also, there is no new cost as in the case of using a temperature sensor. For example, assuming that the operation guarantee minimum temperature is 0 ° C., which is a growth rate of 1000 μm / sec, a voltage application time of 0.16 seconds or more is sufficient for a liquid crystal panel having a pixel size of 160 μm × 50 μm at 0 ° C. For a liquid crystal panel having a pixel size of 450 μm × 150 μm, 0.45 seconds or more was sufficient.

The voltage for the transfer process is applied intermittently or continuously. Here, when intermittently applied the sum of the time of applying, corresponding to T ₁ shown in FIG. Although there is a time lag from the start of the voltage application to the generation of the transition nucleus of the bend orientation, empirically, it was sufficient to set the voltage application time to twice the calculated value based on the growth rate including the margin. . Further, in this embodiment, before the voltage application time indicated by T ₁ in FIG. 2, provided rest period T ₀ of the applied voltage to 0V. By providing this rest period, the transition nucleus can be generated stably, and the transition proceeds stably. As the pause period is lengthened, metastasis can progress more stably. Actually, stable transition processing can be performed by setting the pause period to about 0.2 seconds.

Embodiment 2 In this embodiment, an improvement will be described in which unnecessary power consumption is suppressed and a user does not feel discomfort or anxiety.

FIG. 3 shows a schematic configuration of the liquid crystal display device of the present embodiment. This liquid crystal display device is an OCB type liquid crystal display device. The liquid crystal display device 1 includes an active matrix type 7-inch liquid crystal panel 2, a pair of film retarders 8 for optically compensating for low voltage driving and viewing angle expansion,
A backlight 9 for irradiating the pair of polarizing plates 10 and the liquid crystal panel 2 is provided. The liquid crystal panel 2 has a structure similar to that shown in FIG. The control unit 11 controls ON / OFF of a display drive circuit 12 that outputs a drive signal for display at the time of display drive, a transition drive circuit 13 that outputs a voltage pulse for changing the orientation of the liquid crystal layer to bend orientation, and a backlight. And a control circuit 16 for controlling these. Transition drive circuit 13
Is to intermittently apply a high-voltage transfer voltage pulse of, for example, 15 V between the counter electrode 4b and the pixel electrode 4a of the liquid crystal panel 2 to transfer the liquid crystal layer 7 from the splay alignment to the bend alignment. .

In the present liquid crystal display device, it is necessary to apply a voltage for 2 seconds in order for all the liquid crystal layers in all the pixels of the liquid crystal panel 2 to transition to the bend alignment at room temperature. When the main power supply of the liquid crystal display device 1 is turned on, the control circuit 16
Is connected to the terminal A side, and a high voltage transition voltage pulse is applied to the liquid crystal panel 2 from the transition drive circuit 13 for 2 seconds. The transfer of the liquid crystal molecules 7a in the liquid crystal layer 7 is completed by applying the voltage pulse for 2 seconds. When the application of the voltage pulse is completed, the control circuit 16 connects the switch 15 to the terminal B and connects the display drive circuit 12 to the liquid crystal panel 2. The control circuit 16 operates the backlight control circuit 14 in synchronization with the connection between the display drive circuit 12 and the liquid crystal panel 2 to turn on the backlight 9. Thereby, the liquid crystal display device 1
Shifts to the display drive mode.

In the liquid crystal display device according to the present embodiment, the screen intermittently blinks bright and dark during the transition process as in the conventional liquid crystal display device in which the transition voltage pulse is applied after the backlight is turned on. A defective display in which point defects and surface defects appear on the entire surface of the liquid crystal panel is not performed. Therefore, it is also possible to avoid giving the user an unpleasant impression or expecting a failure. Note that, in the present embodiment, an OCB type liquid crystal display device in which liquid crystal molecules in a liquid crystal layer are transferred from a splay alignment to a bend alignment and then displayed is described as an example. In other types of liquid crystal display devices that display after being transferred to a displayable alignment state, and the alignment state is shifted and progresses non-uniformly on the panel surface during the transfer, for example, an FLC type liquid crystal display device and a phase transition type liquid crystal display device Also applies. In addition, by providing a projection on the electrode, or by providing a unique region formed in the liquid crystal alignment film such that the pretilt angle of liquid crystal molecules located there is different from that of the other region, transition can be induced, Transfer can be reliably completed within a preset time.

Here, as the transition voltage pulse, a voltage of, for example, about 25 V higher than the display drive signal in the display state is applied between the electrodes. However, application of this high voltage requires large power consumption during transition. Therefore, when the voltage value of the transition voltage pulse is set to 5 to 6 V, which is equivalent to the display drive signal, it takes about 30 seconds, but it is possible to transition the liquid crystal molecules in the liquid crystal layer from the splay alignment to the bend alignment at a low voltage. did it. That is, it is not always necessary to provide a power supply mechanism for transfer separately from display. Therefore, by making the voltage mode of the transition voltage pulse equal to that of the display drive signal, power consumption is reduced,
Further, the cost of the device can be reduced.

As shown in FIG. 4, a notebook personal computer, a mobile computer, a foldable portable telephone or the like has a cover 17 for covering the liquid crystal panel 2, and a liquid crystal display which needs to be opened when used. In the case of the device, the control circuit 16 can control the connection between the liquid crystal panel 2 and the display drive circuit 12 or the transfer drive circuit 13 in synchronization with opening and closing of the cover 17. When the cover 17 is opened while the main power is on and the cover 17 is closed, the control circuit 16 determines whether or not the transfer voltage pulse needs to be applied to the liquid crystal panel 2.

When it is determined that the application of the transition voltage pulse is necessary, the control circuit 16 operates the switch 15 to connect the liquid crystal panel 2 and the transition drive circuit 13 to the liquid crystal panel 2.
For example, a transfer voltage pulse is applied for one second. After the application of the transition voltage pulse, the control circuit 16 operates the switch 15 to connect the liquid crystal panel 2 and the display driving circuit 12, and further turns on the backlight 9 in synchronization with the operation. The display shifts to the display drive mode. On the other hand, when it is determined that the application of the transition voltage pulse is unnecessary, the control circuit 16 operates the switch 15 to operate the liquid crystal panel 2 and the display drive circuit 1.
2 and the backlight 9 is turned on in synchronization with this, and the apparatus shifts to a normal display drive mode. When the cover 17 is closed when the main power supply of the apparatus is turned on, the control circuit 16 operates the switch 15 to connect the liquid crystal panel 2 and the transition drive circuit 13 to bend the liquid crystal panel 2. Voltage pulse is applied to maintain In addition, the backlight is turned off in synchronization with it.

When the input from the user is not recognized for a predetermined time, the control circuit 16 similarly operates the switch 15.
Is operated to connect the liquid crystal panel 2 and the transition drive circuit 13, and a voltage pulse is applied to the liquid crystal panel 2 to maintain the bend alignment. In addition, the backlight is turned off in synchronization with it. When an input from the user is confirmed, the control circuit 1
The switch 6 operates the switch 15 to connect the liquid crystal panel 2 and the display drive circuit 12, and further turns on the backlight 9 in synchronization with the operation, whereby the apparatus shifts to a normal display drive mode. These are useful for driving notebook personal computers, mobile computers, foldable mobile phones, and the like.

For example, in a liquid crystal display device having a speaker, such as a liquid crystal television, the speaker is used as means for notifying the progress or end of the transition. When the main power of the apparatus is turned on, a voltage pulse is applied for a predetermined time (for example, 2 seconds). For example, during this transition driving, a sound signal notifying the progress of the transition is output from the speaker. That is, a sound is output from the speaker before the backlight is turned on after the transfer is completed, and it is recognized that the apparatus is being activated even during the transfer operation. In LCD television,
For example, when the main power supply is turned on, the output of the broadcast audio from the speaker is started, and the audio signal notifying the transition state is superimposed on the broadcast audio signal. When the image display and the sound output are started after the end of the transfer, the time lag from when the power is turned on to when the image display and the sound output are started may be a cause of anxiety to the user. Therefore, it is desirable to avoid such anxiety by outputting a sound prior to the image display after the power is turned on. When the transition drive is completed, the sound signal for notifying the end of the transition is output from the speaker along with turning on the backlight and shifting to the display drive mode. Of course, the sound may be output after the backlight is turned on.

Also, the small lamp, light emitting diode, EL element, etc. are turned on as a mark for notifying the user that the transfer process is in progress or the transfer is completed until the backlight is turned on. May be turned on. As a result, the user can be relieved without thinking that the malfunction has occurred. Although the configuration becomes complicated, a transition drive circuit may set a transition completion time in advance, and a means for visually observing the liquid crystal panel and determining the end of the transition to the bend alignment may be provided. Although the backlight is turned on after the transition drive operation, it does not necessarily have to be immediately after. Alternatively, it may be turned on only when the liquid crystal panel is in the display drive mode. In the present invention, a transmissive liquid crystal display device has been described. However, as a driving method of a reflective liquid crystal display device, there is no problem in using a front light instead of a backlight.

<< Embodiment 3 >> In this embodiment, an example of a liquid crystal display device capable of completing the above-mentioned transition more reliably and in a shorter time and shifting to the display driving mode will be described.

FIG. 5 schematically shows the structure of the liquid crystal display device of the present embodiment. This liquid crystal display device includes a so-called active matrix type liquid crystal panel 2 in which switching elements are arranged for each pixel, a pair of polarizers 10, and a phase compensator 8 for optical compensation. The liquid crystal panel 2 has a pair of substrates 3a and 3b facing each other. On the array substrate 3a, a pixel electrode 4a and a switching element 18 composed of, for example, a TFT are arranged. The counter electrode 4b is provided on the counter substrate 3b.
Is arranged. The surfaces of the pixel electrode 4a and the counter electrode 4b are covered with liquid crystal alignment films 6a and 6b, respectively. The liquid crystal alignment films 6a and 6b are both formed by printing and applying a polyamic acid type polyimide alignment film material (manufactured by Nissan Chemical Industries, Ltd., SE-7492), baking, and further rubbing. The liquid crystal layer 7 is filled with a nematic liquid crystal material having a positive dielectric anisotropy. In addition, a spacer (not shown) having a diameter of about 5 microns is provided for keeping the substrate gap constant. Each of the alignment films 6a and 6b has a liquid crystal molecule on its surface of about 5 to 5 so that the liquid crystal molecules form a so-called splay alignment composed of an alignment region in which the liquid crystal molecules are obliquely spread under no voltage application state.
The rubbing directions are arranged parallel to each other so that the pretilt angle is 6 degrees and the molecular axes are located in the same plane.

The temperature detector 19 disposed in close contact with the liquid crystal panel 2 detects the temperature of the liquid crystal panel 2 and outputs a temperature detection signal to the transition drive circuit 13. In addition, the temperature detector 1
When it is difficult to arrange the temperature sensor 9 in close contact with the liquid crystal panel 2, the temperature detector 19 is arranged near the liquid crystal panel 2.
That is, the ambient temperature of the liquid crystal panel may be used as the temperature of the liquid crystal panel. The transition drive circuit 13 determines the condition of the transition voltage pulse applied between the pixel electrode 4a and the counter electrode 4b of the liquid crystal panel 2 based on the temperature detection signal. The transition drive circuit 13 includes a counter electrode 4b and a pixel electrode 4a.
During this time, a transition voltage pulse having a 50% duty cycle shown in FIG. 6 is applied.

It is to be noted that an initial period is provided immediately after the start of the transfer operation, in which the initial voltage between the two electrodes is substantially 0 V (0 V ± 0.5 V). Further, the voltage in the voltage pulse interval period was set to almost 0 V (0 V ± 0.5 V) as in the initial period. Using a liquid crystal display device similar to the liquid crystal display device of this embodiment, −
In an atmosphere of 10 ° C. to 60 ° C., the voltage value of the transition voltage pulse is set to −15 V, −20 V, or −30 V, and the frequency is set to 0.5 Hz, 1 Hz, 3 Hz, or 5 Hz. The transfer time to completion of transfer was evaluated. Tables 2 to 4 show these results.
Shown in

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

[Table 4]

Hereinafter, the liquid crystal display of the present embodiment will be described based on the result of the temperature dependence of the transition time.

[3.1 Frequency Change] The transition drive operation circuit 13 determines the temperature of the liquid crystal panel 2 based on, for example, the temperature of the liquid crystal panel 2 (or the surrounding temperature) detected by the temperature detector 19 and Table 5 below. The frequency of the transfer voltage pulse applied between the electrodes is determined.

[0058]

[Table 5]

The frequency of the transition voltage pulse is continuously changed so that the lower the panel temperature, the lower the frequency. Thereby, the transition process to the bend alignment can be completed in a maximum of 2 seconds. In fact, -10 to 60
When a voltage pulse was applied between the counter electrode 4b and the pixel electrode 4a in the temperature range of 20 ° C., the transition to the bend alignment was completed in a temperature range of 20 ° C. to 60 ° C. at a frequency of several Hz in less than 1 second. In the temperature range of -10 ° C to 0 ° C, the transition was completed in 2 seconds at a low frequency of 1 Hz or less. That is, by detecting the temperature of the liquid crystal panel and determining the frequency of the transition voltage pulse based on the detected temperature, the temperature can be reduced to 0 ° C. or less in a wide temperature range from room temperature to a high-temperature atmosphere in less than 1 second. The transition to bend alignment can be completed in a short time of 2 seconds even in an atmosphere.

When a voltage pulse having a frequency fixed to several Hz is used in the entire operating temperature range as in the conventional OCB type liquid crystal display device, it takes less than one second at a high temperature, but requires several seconds to several tens of seconds at a low temperature. Transition to the bend orientation
It can be completed in an extremely short time in a low-temperature to high-temperature atmosphere, and it is possible to shift to the display mode faster. Although it depends on the liquid crystal material used and the configuration of the liquid crystal panel, generally, in a high temperature range of 20 ° C. to 60 ° C., the frequency is set to 2 to 5 Hz, preferably 2 to 4 Hz to complete the transition in 1 second or less. -10 ° C to 0 ° C
In the low temperature region, the transition can be completed in about 2 seconds by setting the frequency to 0.2 to 1 Hz, preferably 0.4 to 0.6 Hz. Needless to say, the voltage value does not need to be -30 V, and voltage pulses having different voltage values may be applied depending on the material used, the cell gap, and the like, and the configuration of the liquid crystal panel.

In order to complete the transition in a short time, the voltage between the two electrodes must be set to 0V before the application of the voltage pulse.
It is useful to provide an initial period. Ideally, it is desirable to be 0V, but practically 0V ± 0.5
It may be about V. It is also useful to set the voltage between the electrodes between repeated pulses to 0V ± 0.5V, preferably 0V. This effect is exhibited particularly in a low-temperature atmosphere. Immediately before the start of the transfer operation and during the voltage pulse interval, if there is a potential difference of, for example, about -1 V between the two electrodes, the potential difference keeps the liquid crystal molecules in a stable non-uniform splay alignment. Transition nuclei at the time of crystallization
The frequency of occurrence of the occurrence is significantly reduced. Therefore, it is necessary to repeat the pulse voltage more than in a case where a period in which the voltage between both electrodes is substantially 0 V is provided. For the same reason, it is preferable to provide a sufficient initial period and a pulse interval period.

For example, for a voltage pulse having a duty cycle of 50% and a frequency of 0.5 Hz, the initial period is 1 second, the duty cycle is 50% and the frequency is 1
In the case of the voltage pulse of Hz, the initial period is set to 0.5 second. For a voltage pulse having a frequency of 3 Hz, the initial period is set to 0.16 seconds. Although the practical initial period is in the range of about 0.2 to 2 seconds depending on the configuration of the panel and the liquid crystal material, it is necessary to lengthen this initial period to about 2 to 5 seconds to achieve stable transition. Useful for. Note that if the inter-electrode voltage is maintained at 0 V before the start of the transfer process, for example, when the main power supply of the apparatus is turned off, the initial period after the start of the transfer process can be shortened.

[3.2 Change of Voltage Value] By changing the voltage value of the voltage pulse in accordance with the panel temperature, the transition can be similarly performed in a short time. The transition drive circuit 13
Based on the signal from the temperature detector 19, that is, the panel temperature, the frequency of the transition voltage pulse applied between the electrodes is set to 0.
After setting the frequency to 5 Hz, the voltage value is determined as shown in Table 6 below. That is, the voltage value of the transition voltage pulse is continuously changed so as to increase as the panel temperature decreases.

[0064]

[Table 6]

When a voltage was actually applied between the two electrodes under the conditions determined based on the above table, the voltage was -20 V or more in the temperature range of 20 ° C. to 60 ° C. and -20 V or less in the temperature range of -10 ° C. to 20 ° C. By applying a voltage pulse for transfer having a voltage value of, the transfer was completed in one pulse application, that is, 2 seconds within the entire temperature range. That is, as described above, by detecting the panel temperature and applying a transition voltage pulse having a voltage value determined according to the panel temperature, the bend orientation can be changed to a bend alignment in a short time of 2 seconds in a wide temperature range from a low temperature to a high temperature. The transfer can be completed. That is, it is possible to shift to the display drive mode in a very short time even at a low temperature. Note that the voltage value and frequency of the voltage pulse are determined by the liquid crystal material used, the configuration of the cell, and the like.

In the present embodiment, the frequency of the transition voltage pulse is set to 0.5 Hz, and in practical judgment, the initial period immediately after the start of the transition operation is set to 1 second. It is effective to set it to about seconds. The time range of the initial period varies depending on the material and temperature, but is about 0.2.
~ 5 seconds. This initial period may be set before starting the transfer process. In this case, since a substantially sufficient initial period can be provided before the start of the transfer process, the initial period set after the start of the transfer process may be short. Although the ideal initial voltage is preferably 0V, it may be set to about 0V ± 0.5V.

[3.3 Changing Frequency and Voltage Value] Even when both the frequency and the voltage value of the transition voltage pulse are changed according to the ambient temperature, the transition can be completed in a short time from a low temperature to a high temperature. Can be done. For example, Table 7 below
The frequency and the voltage value are determined as shown in FIG.

[0068]

[Table 7]

If the duty cycle, ie, the pulse width, of the voltage pulse is different, the transition time will vary significantly. Also, the duty cycle at which the transition time is minimized differs according to the panel temperature. Therefore, even if the pulse width is changed according to the temperature in place of the above-described frequency and voltage value,
The transition time can be shortened. As described above, when the conditions such as the voltage frequency and the voltage value are continuously changed according to the panel temperature, the optimum voltage pulse condition can be obtained. However, the configuration of the transition drive control circuit for that purpose becomes complicated. Become. Therefore, for example, as shown in Table 8, when the guaranteed use temperature range is divided into two and the condition of the transition voltage pulse is set for each of the divided temperature ranges, the transition time at a low temperature is slightly longer. However, the configuration of the transition drive control circuit is simplified.

[0070]

[Table 8]

Of course, the guaranteed use temperature range may be divided into three or more temperature ranges. As described above, the transition time can be shortened in a wide temperature range by applying the transition voltage pulse including the voltage value, the voltage frequency, the pulse width, or a plurality of these values determined according to the panel temperature.

[3.4 Fixed to Minimum Temperature] In the above-described embodiment, the method of determining the condition of the transition voltage pulse according to the panel temperature has been described. An example of a driving method capable of shortening the transition time even in an atmosphere will be described. In a low temperature atmosphere, it takes a longer time to complete the transition than in a high temperature atmosphere. Therefore, the minimum operating temperature of the device is -10.
The voltage pulse for transition under the condition that the transition can be completed in 2 seconds which is the shortest at 2 ° C., that is, the voltage value is −30.
By applying a transition voltage pulse between both electrodes at V and a voltage frequency of 0.5 Hz, it was possible to transition in at least 2 seconds over a wide temperature range from −10 ° C. to 60 ° C. in transition time. .

In the above embodiment, by setting the frequency of the transition voltage pulse to 0.5 Hz, the application of one negative transition voltage pulse, that is, the transition can be completed in 2 seconds, The optimum frequency differs depending on the liquid crystal material and the configuration of the liquid crystal panel. Generally, the frequency is 0.2-1H
By selecting from the range of z, desirably from 0.4 to 0.6 Hz, the transition can be completed in a shorter time. Depending on the conditions, the voltage pulse for transition may be 1
It is necessary to apply more than a pulse. In the above embodiment, the minimum use temperature is set to -10 ° C, but the minimum use temperature is guaranteed depending on the configuration of the apparatus.

[0074]

According to the present invention, in a liquid crystal display device in which the initial alignment of liquid crystal molecules is different from the alignment for display, the transition of the alignment of the liquid crystal for display can be completed reliably and in a short time. An apparatus and a driving method thereof can be provided.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a growth rate of a liquid crystal alignment film,
(A) shows the relationship between the rubbing direction of the liquid crystal alignment film and the growth rate of the bend alignment phase, and (b) shows the relationship between the applied voltage and the growth rate of the bend alignment phase.

FIG. 2 is a characteristic diagram showing a waveform of a transition voltage pulse.

FIG. 3 is a schematic diagram illustrating a configuration of a liquid crystal display device according to one embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a liquid crystal display device according to another embodiment of the present invention.

FIG. 5 is a schematic view showing a configuration of a liquid crystal display device according to still another embodiment of the present invention.

FIG. 6 is a characteristic diagram illustrating a waveform of a transition voltage pulse applied to a liquid crystal layer in the same example.

FIG. 7 is a schematic longitudinal sectional view of a main part showing a configuration of an OCB type liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal panel 3a Array substrate 3b Counter substrate 4a Pixel electrode 4b Counter electrode 6a, 6b Liquid crystal alignment film 7 Liquid crystal layer 7a Liquid crystal molecule 8 Phase compensator 9 Backlight 10 Polarizer 11 Control part 12 Display drive circuit 13 Transition Drive circuit 14 Backlight control circuit 15 Switch 16 Control circuit 17 Cover 18 Switching element 19 Temperature detector

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI G09G 3/20 G09G 3/20 670L 3/34 3/34 J 3/36 3/36 (72) Inventor Tsuyoshi Uemura Kadoma, Osaka 1006 Kadoma, Ichidai-shi Matsushita Electric Industrial Co., Ltd. Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Mika Nakamura 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Junichi Kobayashi 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric (56) References JP-A-9-185037 (JP, A) JP-A-7-5427 (JP, A) JP-A-2-10408 (JP, U)

Claims (12)

(57) [Claims] 1. A pair of substrates, a liquid crystal sandwiched between the pair of substrates, an initial alignment state being a splay alignment state, and an alignment state at the time of display being a bend alignment state, and a voltage applied to the liquid crystal. And a backlight for irradiating the liquid crystal panel with light for displaying the liquid crystal panel, wherein the liquid crystal is in a splay alignment state. At one time, a transition step of applying an AC voltage of 0.5 Hz or less to the liquid crystal to transition the liquid crystal to the bend alignment state, and a lighting step of lighting the backlight, wherein the transition step is performed. A driving method of the liquid crystal display device, wherein the lighting step is not performed. 2. The method according to claim 1, wherein when a predetermined time has elapsed from the start of the application of the voltage for the transition of the liquid crystal layer, the transition is determined to be completed, and the application of the voltage is terminated. 2. The method of driving a liquid crystal display device according to claim 1, wherein: 3. The method of driving a liquid crystal display device according to claim 1, wherein the liquid crystal display device further comprises a cover for covering a display unit of the liquid crystal panel, and the transition step is started in synchronization with opening of the cover. 4. The liquid crystal display device further comprises a cover for covering the liquid crystal panel, for turning off the backlight and maintaining the alignment state of the liquid crystal layer in synchronization with the closing of the cover during display driving. Applying a voltage to the liquid crystal layer, turning on the backlight in synchronization with opening of the cover during application of the voltage for maintaining the alignment state of the liquid crystal material, and terminating the application of the voltage. And driving the liquid crystal display device. 5. A voltage is applied to the liquid crystal layer in order to turn off the backlight and maintain the alignment state of the liquid crystal layer when no input signal from the user is recognized for a predetermined time during display driving. The method according to claim 1, further comprising the step of: 6. The method according to claim 1, further comprising, when an input signal from the user is detected during application of the voltage for maintaining the alignment state of the liquid crystal material, ending the application of the voltage and turning on a backlight. 6. The driving method for a liquid crystal display device according to claim 5, comprising: 7. A pair of substrates, a liquid crystal sandwiched between the pair of substrates, an initial alignment state being a splay alignment state, and an alignment state at the time of display being a bend alignment state; and applying a voltage to the liquid crystal. And a backlight for irradiating the liquid crystal panel with light for display on the liquid crystal panel, wherein the voltage is applied to transition the liquid crystal from a splay alignment state to a bend alignment state. A transition control unit that drives an application unit to apply a voltage of 0.5 Hz or less to the liquid crystal in the spray state, and when a transition operation is performed by the transition control unit,
A liquid crystal display device comprising: a backlight control unit that does not turn on the backlight. 8. The liquid crystal display device according to claim 7 , wherein said transition control means determines that said transition has ended when a predetermined time has elapsed from the start of application of said voltage for said transition of said liquid crystal layer. 9. comprising further a cover for covering the liquid crystal panel, the transition control means, in synchronism with the opening of the cover according to claim 7, wherein starting the application of the voltage for transferring the liquid crystal layer Liquid crystal display. 10. A cover for covering a display portion of the liquid crystal panel, and the transition control means for turning off the backlight in synchronization with closing of the cover and maintaining an alignment state of the liquid crystal layer. And a switch for applying a voltage to the backlight, turning on the backlight in synchronization with opening of the cover, and terminating the application of the voltage.
8. The liquid crystal display device according to 7 . 11. The image forming apparatus according to claim 1, wherein the transition control unit determines that an input signal from a user is not recognized for a predetermined time during display driving.
8. The liquid crystal display device according to claim 7 , wherein the voltage application unit is driven to maintain the alignment state of the liquid crystal layer, and the backlight control unit turns off the backlight. 12. The liquid crystal display device according to claim 7 , further comprising a switch for forcibly starting application of a voltage for shifting the liquid crystal layer by the voltage applying unit.